Boletín de aludes

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Sawtooth Avalanche Center
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Peligro de aludes

Thu
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You are most likely to trigger avalanches large enough to bury people at upper elevations and on middle elevation slopes facing the northern half of the compass. You may not observe obvious warning signs—recent avalanches or snowpack cracking or collapsing—before triggering a slide.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5

    What and where is it?  1.5-2.5 foot thick slabs lie above persistent weak layers: crumbly facets or crust + facet combinations. Until proven otherwise, assume the old, weak layers exist near the bottom of the snowpack on all upper elevation slopes and on shadier middle elevation slopes (W-NW-N-NE-E aspects).  Slopes where the wind recently formed drifts are especially suspect. 

    How can you recognize it? On shadier aspects, you can easily feel the old crusts and sugary facets with your hands, ski pole, or snowmobile track (see photos and videos below). On sunnier aspects, the weak layers present as a series of crusts and facets and are not as obvious. 

    How can you manage it?  Sadly, the only surefire way option is to avoid avalanche terrain where denser slabs rest above the weak, older facets and crusts. Short of that, you can reduce your risk by avoiding recently wind-loaded slopes, large avalanche paths, and those with ugly consequences if you are caught in a slide. Persistent Slab avalanches can break wider and higher on slopes (above you!) than you might expect. Several skiers or riders can descend a slope, only to have the next person trigger an avalanche.

    ADDITIONAL DISCUSSION:  Watch for thin, fresh wind slabs near ridgelines in exposed terrain. Although small, these slabs could overlie facets, crusts, or surface hoar that make the slabs easy to trigger. Small avalanches can carry you where you don't want to go and can be effective triggers for much larger avalanches failing on the weak snow near the ground. 

Avalanche Discussion

Recent observations show a slow, gradual trend of decreasing "red flags"—recent avalanches, snowpack collapsing and cracking— and we have not oberved or received reports of large avalanches in a couple weeks. But, avalanche professionals and experienced recreationists don't trust the facets and crust + facets near the bottom of the snowpack and remain hesitant to sample the goods in avalanche terrain. People continue reporting poor snowpack test scores and are avoiding travel in large or consequential avalanche starting zones. In recent days, some folks have dabbled in smaller avalanche paths with runout zones free of trees, cliffs, or creeks. 

Generally speaking, snowpacks stabilize over time following a loading event. The chance of triggering large avalanches slowly decreases each day without significant snowfall or wind-loading.  However, the Persistent Slab avalanche problem earned its name by lulling travelers to sleep for days before rearing its ugly head. 

Could you "get away" with playing in big, consequential avalanche terrain? Maybe. Could several members of your group ski or ride a slide path with no trouble, only to have the last person trigger a large slide and get buried or injured? Yes.  

Playing in steep terrain today is similar to playing a game of blackjack or "21": If you have a good enough hand to beat the dealer and the dealer has to draw a card, the odds are in your favor. But, the dealer could draw the card they need to win and take your money. The difference in the mountains: we are playing with our health and lives instead of money.

What's the good news? If you don't understand the game (Persistent Slab avalanches) that well or are not comfortable losing, you don't have to play; you get to choose where you ski or ride.

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